Diffuse Reflectance Infrared Spectroscopic Characterization of Silica Dehydroxylation

Abstract

Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) is employed to study the dehydroxylation of amorphous silica. Dehydroxylation results in the appearance of infrared absorption bands at 1022, 1107, and 1240 cm⁻¹ assigned to asymmetric stretching vibrations for three different siloxane bridge types. The 1107-cm⁻¹ absorbance band represents a siloxane bridge that is indistinguishable from bulk species. The 1022-cm⁻¹ absorbance band represents a siloxane bridge with a bond angle that is smaller than the bulk, with little change in the stretching vibration force constant. The 1240-cm⁻¹ absorbance band derives from a siloxane bridge characterized by a stretching force constant significantly larger than that of bulk siloxane bridges. This band may be indicative of a highly strained or broken siloxane bridge.